Molecular electronics monolayers

Reactions on the surface are interesting. The adsorptions of unsaturated organic molecules on the surface provide a means for fabricating well-ordered monolayer films. Thin film organic layers can be used for diverse applications such as chemical and biological sensors, computer displays, and molecular electronics. 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

To extract useful results from a molecular electronic device, or just to measure its electronic characteristics, connections must be made to macroscopic probes. That is, metallic electrodes must interface to different ends of the molecule of interest. An experiment may interrogate a single molecule, or may measure a one-molecule-thick layer, i.e., a monolayer, of the molecules of interest, provided all the molecules are oriented in the same direction. In either case, several questions arise. What is the nature of the contact between metal and molecule(s) What metal should be chosen, and what should be the form or shape of this electrode ... 

Ranganathan S, Steidel I, Anariba F, McCreery RL (2001) Covalently bonded organic monolayers on a carbon substrate a new paradigm for molecular electronics. Nano Lett 1 491 194... 

M. Buck reviews in great depth the literature on self-assembled monolayers (SAMs) of thiols on gold, a classic means of surface modification. The wide variety of functional groups that is provided by synthetic chemists makes thiol-SAMs an exciting playground for applications where the gap between two worlds, the inorganic and the organic, needs to be closed. Examples are molecular electronics and biochemistry. 

Xie R, Bryant GW, Zhao J et al (2003) Tailorable acceptor Cgo-nBn and donor Cgo-niNm pairs for molecular electronics. Phys Rev Lett 90 206602/1-206602/4 Metzger RM (2003) One-molecule-thick devices rectification of electrical current by three Langmuir-Blodgett monolayers. Synth Met 137 1499-1501... 

Keywords Metal vapor deposition Metal-organic interface Molecular devices Molecular electronics Self-Assembled Monolayers... 

Zhou C, Nagy G, Walker AV (2005) Toward molecular electronic circuitry selective deposition of metals on patterned self-assembled monolayer surfaces. J Am Chem Soc 127 12160-12161... 

Seitz O, Dai M, Aguirre-Tostado FS, Wallace RM, Chabal YJ (2009) Copper-metal deposition on self assembled monolayer for making top contacts in molecular electronic devices. J Am Chem Soc 131(50) 18159-18167... 

The LB deposition is one of the best methods to prepare highly organized molecular systems, in which various molecular parameters such as distance, orientation, extent of chromophore interaction, or redox potential can be controlled in each monolayer. We have been studying photophysical and photochemical properties of LB films in order to construct molecular electronic and photonic devices. The molecular orientation and interactions of redox chromophores are very important in controlling photoresponses at the molecular level. Absorption and fluorescence spectra give important information on them. We have studied photoresponses, specific interactions, and in-plane and out-of-plane orientation of various chromophores in LB films [3-11], In addition to the change of absorp-... 

Langmuir-Blodgett Monolayers in Molecular Electronic Devices... 

While electrochemical experiments provide useful information regarding electron transport through these molecular monolayers, construction of real devices requires formation of a top contact so that solid-state transport measurements can be made. The fabrication of contacts to molecular layers has been the major obstacle to the development of molecular electronic devices, whether based on thiol-based SAMs on gold or covalently attached molecules on silicon. The most popular approach to making contacts involves evaporation of metals onto the molecular layer, which is likely to result in at least partial penetration of the monolayer, and may possibly damage the molecules in the layer. 

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